What are termed ultra wideband signals (UWB signals) are transmitted in a frequency range from 3.1 GHz to 10.6 GHz. A proposal for a new UWB transmission standard makes provision for this frequency range to be divided into 16 sub-bands or frequency bands each with a width of 538 MHz, as is shown schematically in FIG. 9. f1-f16 denote the frequency bands in this case or their center frequencies; f means frequency. Pieces of data, which may for example be intended for a plurality of users or for different blocks within a receiver, can then be transmitted separately in respective ones of the different frequency bands.
What are usually used in this case are the bottom eight sub-bands f1-f8. FIG. 10 shows a typical transmission signal under this proposed standard. The information to be transmitted is transmitted in this case in the form of short pulses of length Tp, with the pulses for the different frequency bands being transmitted serially. The sequence f1, f6, f3, etc. shown in FIG. 10 is of course only one possibility. The pulse length Tp may for example be selected in this case in such a way that it is equal to the inverse of the width of the frequency bands. Each pulse corresponds for example to one bit, with the information being coded in each case by binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK). The bit rate is therefore determined by the time Tb required to transmit a pulse in each frequency band that is used. The distance between the beginnings of two successive pulses, which corresponds to the bit rate, is marked as Tr in FIG. 10.
FIG. 11 shows an analogue section of a conventional receiver for signals of this kind. The received signal a is received by an antenna 1 in this case and is fed to a filter 22. It is then amplified by a low-noise amplifier (LNA) 2 and a variable-gain amplifier 3. The amplifier 3 may be used in this case in particular to set gain as a function of the strength of the received signal a.
Having been amplified in this way, the signal is fed to N units 27, where N is the number of frequency bands to be processed, which is eight in the example shown in FIG. 10. Each of the units 27 separates out one of the frequency bands. This is done by in each case mixing the amplified received signal in a mixer 23 with a signal LOi (i=1 . . . N) generated by a local oscillator. A bandpass filter 24 then filters out that component part of the mixed signal which corresponds to the difference between the frequency of signal LOi and the frequency of the particular frequency band fi. The frequencies of the signals LOi are preferably selected in this case in such a way that all the filters 24 can be of the same design. The signal is then amplified by a programmable amplifier 25 and digitized by means of an analogue-to-digital converter 26. The digitized signal is then subjected to further processing.
A receiver of this kind is relatively costly and complicated to implement because the unit 27 has to be provided for each frequency band fi, which means that in the example shown eight analogue-to-digital converters are required.